With the rapid development of wireless communication techniques, personal mobile phone data card (e.g., mobile phone, data card, MiFi/Hotspot) has been extensively popularized and applied. In a daily application scenario, a distance between such a product and a human body has become smaller and smaller, therefore the impact of electromagnetic radiation induced by the mobile phone data card on human health becomes a matter of public concerns.
Generally, a SAR indicator is applied to measure energy absorbed by the human body under electromagnetic exposure environment around the world. Many countries formulate relevant laws and regulations, in which an upper limit of the SAR value of the mobile phone data card is limited to ensure the safety of the electromagnetic radiation to the human body. For instance, Federal Communications Commission (FCC) explicitly regulates the maximum allowable SAR of various wireless mobile terminals when interacted with the human body. In the light of the regulation, for a product such as the mobile phone, a SAR peak value must not exceed 1.6 mW/g when placed close to a side of the human brain; for a product such as the data card, the SAR value must not exceed an upper limit of 1.6 mW/g (1.2 mW/g is suggested) near the whole surface of the product which is probably contacted by the human body. In 2010, the FCC has further put forwarded a regulation relevant to the SAR value on the MiFi (a portable broadband wireless apparatus) and Hotspot (a wireless hot spot).
As shown in FIG. 1, it is a schematic diagram illustrating a planar structure of a wireless mobile phone data card. The existing mobile phone data card consists of an antenna 1, a feed source 2, and a radio frequency (RF) substrate 3, where both the antenna 1 and the RF substrate 3 are made of metal material, and the antenna is configured to transmit and receive a signal, and the feed source connected between the RF substrate and the antenna is configured to excite the antenna. A distance from the feed source 2 respectively to an end of a short side and an end of a long side of the RF substrate 3 is distance 4 and distance 5, respectively. When the antenna 1 is operated, a result excited by the antenna 1 and the RF substrate 3 is that: a high-frequency current flows in the RF substrate 3; due to different electrical lengths in two directions, i.e., the short side and the long side, the excited currents in the RF substrate 3 flow in a same direction and cannot be dispersed, and thus leading to a very high current peak on the RF substrate, which in turn results in a relative higher SAR value.
Existing methods for reducing SAR peak value are generally achieved at the expense of the communication quality of the antenna. For example, the SAR peak value may be reduced by reducing an output power lever of a RF power amplifier or by placing a wave-absorbing material inside the terminal and coating a wave-absorbing layer. In addition, another method is provided by arranging a conductor-reflector and a shielding device in the mobile phone data card to isolate the electromagnetic wave from the antenna to the side of the human body.
However, by means of the measures such as the unilateral reflector mentioned above, the radiation from the antenna to one side of the human body is reduced, while the radiation to the other side is enhanced. Therefore, the use of the reflector is more applicable for the products such as mobile phones rather than the data cards. Further, the reflector and the shielding device need a greater space during an assembling process, and thus cannot satisfy the requirement of miniaturization design for the mobile phone data card.